OFF – Deactivates the fuel pump. The corresponding LOW PRESSURE lights are disarmed when the Center Tank Pump switches are OFF.
ON – Activates the fuel pump. The corresponding LOW PRESSURE lights are armed and will illuminate if a low fuel pressure condition exists.
Center tank pumps produce higher pressure than main tank pumps. This ensures that center tank fuel is used before main tank fuel, even though all fuel pumps are operating.
Both engines are normally pressure fed from the center tank until the center tank quantity decreases to near zero. The engines are normally then pressure fed from their respective main tanks.
Center Tank Fuel Scavenge Jet Pump With the main tank fuel pump No. 1 FWD Switch ON, the center tank fuel scavenge jet pump operates automatically to transfer any remaining center tank fuel to main tank No. 1. Fuel transfer begins when main tank No. 1 quantity is about one-half. Once the fuel scavenge process begins, it continues for the remainder of the flight.